Through disease or injury, the laminae, spinous process, articular processes, or facets of one or more vertebral bodies can become damaged, such that the vertebrae no longer articulate or properly align with each other. This can result in an undesired anatomy, loss of mobility, and pain or discomfort. For example, spinal stenosis, as well as spondylosis, spondylolisthesis, osteoarthritis and other degenerative phenomena may cause back pain, especially lower back pain, such as in the lumbosacral (L4-S1) region. Such phenomena may be caused by a narrowing of the spinal canal by a variety of causes that result in the pinching of the spinal cord and/or nerves in the spine.
The prior art has many spinal prostheses designed to help the patient with various back problems. One problem addressed by the prior art is that of the spinal lordosis.
A normal and healthy spine has a natural curvature referred to as lordosis. As a result of the curvature, opposing vertebrae are positioned with their end plates in nonparallel alignment depending upon the position in the spine. For example, in the lumbar region of the spine, the end plates of the L-4 and L-5 vertebrae may be at an angle of about 3-15°. Similarly, the opposing end plates of the L-5 and S-1 vertebrae may have a lordotic angle of about 8-16°. The actual amount of lordosis varies with the location of the spine and varies from patient to patient.
A problem that needs to be addressed in spinal prosthetic devices is that of matching or correcting the lordotic angle. The prior art accomplishes this with custom-built prostheses with a predetermined lordotic angle.
For example, U.S. Pat. Nos. 6,740,091 and 6,165,219 to Kohrs, et al., assigned to Sulzer Spine-Tech Inc. (Minneapolis, Minn.) describe a lordotic implant that has a frustoconical shape with external threads. Prior to placement of the implant, vertebrae are distracted in a manner to provide a desired lordosis between the vertebrae. The pre-distracted vertebrae are then tapped to provide a tapped bore having a geometry matching the conical geometry of the implant. The threaded implant is then placed within the pre-tapped conical bore.
US Patent Application 20030028250 to Reilley et al., describes cephalad and caudal vertebral facet joint prostheses. The prostheses are customized to provide a pre-defined lordotic angle and a pre-defined pedicle entry angle.
Reilley et al. states that the prostheses can be “adjusted” to create a desired lordotic angle. Quoting from paragraph 27 of Reilley et al., “Various other aspects of the invention provide cephalad and/or caudal prostheses that readily adapt to or physically change the specific anatomy of an individual. For example, a cephalad prosthesis can be capable of being adjusted in either an anterior or posterior direction relative to a vertebra. As another example, a cephalad prosthesis and/or a caudal prosthesis can provide for lateral (left and right) adjustment, to accommodate or create variances in the distance between the right and left pedicles of a single vertebra. Furthermore, a cephalad prosthesis and/or a caudal prosthesis can provide vertical (up and down) adjustment, to accommodate or create variations in interpedicle distance between adjacent vertebra. Or, as another example, a cephalad prosthesis and a caudal prosthesis can together create a desired lordotic angle between adjacent vertebral bodies, or create a pre-defined pedicle entry angle for mounting each prosthesis on a given vertebral body.”
However, the “adjustment” that Reilley et al. provides is nothing more than a prosthesis pre-manufactured and customized to a particular lordotic angle. The “adjustment” means selecting the desired angle and making a fixed, non-adjustable prosthesis according to the selected angle. This is evident, for example, from FIG. 16 of Reilley et al. and the accompanying text in paragraphs 110 and 112-113, which describe “Lordotic Angle Adjustment”: “In the illustrated embodiment (see FIG. 16), the openings 50 and 56 of adjacent cephalad and caudal prostheses 36 and 38 are mutually oriented in nonparallel planes along the inferior-superior axis. The non-parallel orientation of the planes defines between the fixation elements 52 and 58, when supported by the openings 50 and 56, an angle that results a desired lordotic angle. The mutual orientation and the resulting angle defined depends upon the intended location of the prostheses 36 and 38 along the spinal column 10. The defined angle is designated angle “L” in FIG. 16. In FIG. 16, the angle L is defined by orienting the plane of the opening 50 of the cephalad prosthesis 36 generally parallel to the inferior-superior axis, while tilting the plane of the opening 56 of the caudal prosthesis 38 generally downward at an acute inferior angle relative to the inferior-superior axis.” It is noted that “tilting the plane of the opening 56 of the caudal prosthesis 38” does not refer to any in-situ tilting, rather machining the prosthesis to the desired angle.